Among multi-phase power transmission， six-phase transmission is the most feasible one. For the situation of 120 kinds of faults， six-sequence components method， which includes same positive sequence， same negative sequence， same zero sequence， opposite positive sequence， opposite negative sequence and opposite zero sequence， is applied in the fault analysis of six-phase power transmission system， and the transferred sequence components have clearly physical meanings. The same sequences in six-phase transmission power correspond to opposite sequences in parallel transmission lines， and the opposite sequences in six-phase transmission power correspond to the same sequences in parallel transmission lines. Based on six-sequence networks and boundary conditions of various faults， composite sequence networks have been established and the characteristics of each sequence component have been found out when fault happens. In a six-phase transmission system， these characteristics provide the fundamental principle for protection setting. Based on this methodology， a kind of fault phase selection scheme of six-phase transmission system is proposed.